jfet output for f4

[slr 5000]

g,day
i have some populated civiller f4 boards that just need the output devices to be complete

reading about the fw j2 and f2j has got me interested in this type of output for my f4, i think i can get the semisouth devices from this forum

my questions are

1, what type ,semisouth ?

2, can i use 1 pair per channel like the j2 instead of the f4,s 3 pair

3, any other mods ,resistor changes?

4, is it worth doing

they are to power veravox 7x @93db so i only need 10w or so

cheers

 

[Zen Mod]

naah

better wait for J2 or M2 schm

first one with SS , second one with just one pair of F4 outputs (plain mosfets)

 

[slr 5000]

hi Zen mod

many thanks for your fast reply and honesty as usual

you have read my mind ,the j2 is what i really want to build and the above project is just an atempt to temporarely satisfy my bad urges

i also have some populated aleph j boards if these would be better to mod than the f4
cheers

 

[Zen Mod]

make J and enjoy

there is thread started by 6L6 - Papa gave him few 2SJ109BL and SS during last BAF , along with enough info for quick sketch of Aleph J with SS outputs .

even if he (6L6) is silent lately in that thread , I think that's best temporary solution for you ....... 'till Papa give J2 secret in public .

in any case , I can't see any benefit of taking expensive and tricky route - making follower (like F4 - unity gain ) stage with Semisouths , comparing to complementary mosfet follower stage ......

biasing SS is trickier ( vs. plain mosfets , considering that we have just one polarity of SS) and their virtues aren't used in follower stage ........ at least not in that amount as in any stage with gain

also - there is nice thread - contemplating about marriage of "short" F4 - using just one output pair , mated with input xformer .
even if not real McKay , I resume that you'll have enough of M2

soryy - I didn't remember neither who started that thread , nor exact subject

 

[slr 5000]

baad ZEN MOD
now you have me thinking about the m2

i just did some checking and found that Generg has done this

he used electra print transformers

seems quite easy to do with the f4 i already have ,he mentions 1.5 as a transformer ratio

can you advise a suitable transformer

many thanks

 

[slr 5000]

heres a few parts from my diy box😀

i have heaps more proberbly double this

i also have my aleph 2 monoblocks that i love and have been using for 3 years or so

the speakers are diy also

i cant help myself!!

 

[Zen Mod]

yup - I'm aware of Generg's work/fun ;

we had some little collaboration regarding some things (under the bush ) ...... in fact , we started with Lundahls (LL1674 , with which I measured up to 90Vpp broadband , unclipped ) , but Generg later decided that some ( I'm not remembering which ones ) cheaper solutions are even better for his ears .

he's da man whom you can bug for info regarding input autoformer .

considering that you don't even need full blast wattage , Poor Man's M2 will serve you equally well as genuine M2 .

it's charming little devil amp 😉

 

[slr 5000]

cheers Zen Mod

i will bug Generg😀

thanks again

quik q before i go ,do i need 1 or 2 of those transformers for a stereo amp (i,m guessing 2 but what do i know)

 

[Zen Mod]

one per channel , so two .

or just one , if you're going for mono

 

[slr 5000]

thanyou mr Zen

your help is much appreciated

cheers

 

[d to the g]

also - there is nice thread - contemplating about marriage of "short" F4 - using just one output pair , mated with input xformer .
even if not real McKay , I resume that you'll have enough of M2

crippled, liberated, short... lots of names for this F4, but at which point is it snipped? Is it just the jfet input that's discarded, with the input coming in at the intersection of R8/R9 and Q11 (the TL431)? I'm assuming the two 220uF capacitors (C1 and C2) are no longer needed either.

If I'm not mistaken the TL431 is acting as a phase splitter, but a center tapped transformer could just as easily act as such. Unfortunately, my transformers don't have a center tap.

A liberated schematic would be golden here.

 

[Zen Mod]

I just found two schms in my pc

you can use whatever suits you (needing input shunting resistor or not)

those two caps are needed , as they're for \DC decoupling

TL431 is bias gene , so no phase splitting role here

"short" F4 means somewhat as F4 with just one output pair

term based on Papa's words , "output 3 , 4 , 6 deep" , meaning output with 3 , 4 , 6 mosfet pairs

 

[flocchini]

baad ZEN MOD
now you have me thinking about the m2

i just did some checking and found that Generg has done this

he used electra print transformers

seems quite easy to do with the f4 i already have ,he mentions 1.5 as a transformer ratio

can you advise a suitable transformer

many thanks

Can you point me to the thread? I remember seeing it but I cant find it now.
Thanks !!
Bob

 

[d to the g]

Magma front end

Generg also discusses the same amp in the l'amp thread.

Thans zm for the schema. I'll be wiring up in a few minutes.

 

[flocchini]

Magma front end

Generg also discusses the same amp in the l'amp thread.

Thans zm for the schema. I'll be wiring up in a few minutes.

Thank you

 

[buzzforb]

First one includes drain resistor(47K) on FE, important if hooking up to pre with no cap. Fried a DAC not having this one. Just thought i would point that out. What is the official name of that resistor, ZM? Tired of being ignorant of terminology.

 

[Zen Mod]

you can call it Giorgio



or input resistor

or whatever ...... maybe input shunting resistor is best name

or ...... $*it happening Preventer

 

[buzzforb]

Input shunt fits OK and makes sense, at least to me. Giorgio sounds sexier, though!

 

[Zen Mod]

Preventer is too serious , I presume ?

 

[buzzforb]

Perhaps appropriate in the right context.